Interactive touch systems are well known in the art and typically include a touch screen having a touch surface on which contacts are made using a pointer in order to generate user input. Pointer contacts with the touch surface are detected and are used to generate corresponding output based on the locations of contact. There are basically two general types of touch systems available and they can be broadly classified as “active” touch systems and “passive” touch systems.
Interactive touch systems have a number of applications relating to computer operation and video display. For example, U.S. Pat. No. 5,448,263 to Martin, assigned to SMART Technologies Inc., assignee of the present invention, discloses a passive touch system including a touch screen coupled to a computer. The computer display is projected on to the touch surface of the touch screen via an imaging device such as a projector. The coordinates representing specific locations on the touch surface are mapped to the coordinate system of the computer display. When a user contacts the touch surface of the touch screen, coordinate data is generated by the touch screen and fed to the computer. The computer maps the received coordinate data to the computer display thereby allowing the user to operate the computer in a manner similar to using a computer mouse simply by contacting the touch surface. Furthermore, the coordinate data fed back to the computer can be recorded in an application and redisplayed at a later time. Recording the coordinate data generated in response to user contacts is typically done when it is desired to record information written or drawn on the touch surface by the user.
As the projector is separate from the touch surface of the touch screen, steps must be taken to calibrate the touch system thereby to align the projected image of the computer display with the coordinate system of the touch screen. During calibration, calibration marks are projected on to the touch surface and the user is prompted to contact the touch surface at the calibration mark locations resulting in coordinate data being generated. Since the coordinates of the calibration marks in the computer display coordinate system are known, the coordinate data generated by the touch screen in response to the user contacts at the calibration mark locations can be used to map the coordinate system of the touch screen to the computer display coordinate system. This calibration process corrects for projector/touch surface misalignment, and compensates for scale, skew, rotation and keystone distortion.
Contacting the touch surface at least at three calibration mark locations is required to accurately correct for scale, skew and rotational misalignment of a projected image with a planar touch surface. Contacting the touch surface at least at four discrete calibration mark locations is required to accurately correct for keystone distortion. Keystone distortion is generally the result of non-orthogonal axial misalignment between the imaging device used to project the image and the touch surface. Contacting the touch surface at more than four calibration mark locations during the calibration process provides for more robust calibration of the touch system.
It is common for interactive touch systems to have calibration processes requiring user input at up to eighty-one (81) calibration mark locations. Such a calibration process provides a high degree of accuracy but can be quite time consuming and laborious, since care must be taken to contact the touch surface at the exact location of each displayed calibration mark. If the imaging device or touch surface is bumped or moved, the entire calibration process may need to be repeated. As will be appreciated a calibration process for interactive touch systems that can be performed quickly and easily is desired.
Therefore, it is an object of the present invention to provide a novel method and apparatus for calibrating an interactive touch system.